The present invention relates to an optical waveguide junction which can be used as a wavelength demultiplexer. It has a pair of aligned fibers, a partially previous layer arranged between the fibers and diagonally to their axis, and a fiber branching off laterally from the pair of aligned fibers at the level of the intermediate partially pervious layer.
A typical optical waveguide junction is disclosed in U.S. Pat. No. 4,339,290. Junctions of this type can be used as wavelength demultiplexers, if a wavelength-selective filter is used as a partially pervious layer. Demultiplexers of this type have already been proposed.
In the above-mentioned junction, all three fibers are identical, in that they all have the same core diameter and outer diameter. However, junctions and demultiplexers have already been proposed where the aligned fibers are monomode fibers and the branching fiber is a multimode fiber with a considerably larger core diameter than the monomode fibers. Furthermore, the branching fiber must not branch off at right angles to the aligned fibers, as in the case of the typical junction; particularly with regard to demultiplexers, it has proven desirable to arrange the wavelength-selective filter at an angle of inclination to the fiber axis exceeding 45.degree., which requires that the branching fiber runs diagonally to the aligned fiber. In the case of other junctions, particularly demultiplexers, the aligned fibers which are separated by the partially pervious layer always consist of identical fibers. One reason for this is in manufacturing junctions of this type, the aligned fibers are produced by a spacing step in which a carrier for fibers and the fibers attached to it are separated transversely to their axis. Also, the two separated parts, after a partially pervious layer has been supplied to the two polished interfaces thus formed, are reconnected with one another in such a manner that the separated fibers are axially realigned, and the carrier again takes on its original shape.
A separation of this type is possible, because among other reasons the process steps for aligning the axes of the optical waveguides to each other are self-adjusting. This results in a simplification of the production process, and at the same time it results in greater accuracy and reproducibility (see published German Patent Application DE-OS No. 29 20 957 at page 6). In particular, the high degree of accuracy that can be achieved permits a high degree of coupling efficiency between the identical aligned fibers of the junction, and even permits the production of junctions where the aligned fibers consist of monomode fibers, the coupling of which requires particularly high adjusting tolerances, and where the coupling efficiency has clearly defined limits.